Spokeswoman Lori Gamache said the department has notified Washington officials and is investigating the leak further. An engineering analysis team will conduct additional sampling and video inspection to determine the source of the contamination, she said.

State and federal officials have long said leaking tanks at Hanford do not pose an immediate threat to the environment or public health. The largest waterway in the Pacific Northwest — the Columbia River — is still at least 5 miles away and the closest communities are several miles downstream. However, if this dangerous waste escapes the tank into the soil, it raises concerns about it traveling to the groundwater and someday potentially reaching the river.

Washington Governor Jay Inslee said in a statement that the situation ‘‘must be treated with the utmost seriousness.’’